Long-term survival of the plant-growth-promoting bacteria Azospirillum brasilense and Pseudomonas fluorescens in dry alginate inoculant

Two plant-growth-promoting bacteria, Azospirilliun brasilense Cd and Pseudomonas fluroescens 313, immobilized in 1983 in two types of alginate-bead inocuiant (with and without skim-milk supplement) and later dried and stood at ambient temperature for 14 years, were recovered in 1996. The population in each type of bead had decreased, yet significant numbers survived (10(5)-10(6)cfu/g beads). Population numbers depended on the bead type and the three independent bacterial counting methods: the conventional plate-count method, indirect enzyme-linked immunosorbent assay and the limited-enrichment technique. Both bacterial species retained several of their original physiological features. When inoculated onto wheat plants, both species colonized and produced plant-growth effects equal to those of the contemporary strain from a culture collection or to their own 1983 records. This study showed that bacteria can survive in alginate inoculant over long periods.